Images which have been formed on a viewing screen (of either the front-projection or rear-projection type) by projection from projection display devices, such as the one disclosed in U.S. Pat. No. 3,853,614, may suffer from small scale scintillations, or speckle, which appear to move only when the viewer of the image moves his head. This effect is more objectionable in rear-projection screens upon which the image formed on the aforementioned display is projected because the light passing through a typical rear-projection screen retains more of its partial coherence than does the same light when reflected from a typical front-projection screen. Front projection displays are often used for this reason notwithstanding the more complex, less unified system arrangement which is required. The compact system geometries possible with rear-projection systems makes it highly advantageous to find solutions to the speckle problem associated with its use.